In ball sports, such as football, tennis or golf, a ball used and its characteristics represent a significant aspect. Its size, i.e. its diameter or circumference, and its weight are examples of characteristics that belong to such a ball.
In addition, characteristics that are of importance when kicking or hitting the ball are also particularly important. These include, for example, the surface friction (the “grip”) and the stiffness, elasticity, and hardness of the ball or its outer casing, where present.
During the flight of the ball through the air, further characteristics become important. These include imbalances, which could lead to an undesired “flutter” of the ball, and deviations from a spherically symmetrical distribution of mass, which could result in an undesired nutational movement, i.e. a precession. Furthermore, during the flight, the surface properties play a large role for the aerodynamic characteristics of the ball. Thus, a ball rotating in flight can follow a curved trajectory that deviates from a straight trajectory. This effect is generally described as “spin” and its force depends on the surface characteristics of the ball.
Finally, the characteristics of the ball upon impact or bounce are important. For example, a football that hits the lawn or the head of a player, is initially deformed due to its elasticity, i.e. kinetic energy that is converted into potential energy. The ball then aims to return to its original shape. Here the potential energy stored through the deformation is converted back into kinetic energy—the ball bounces off the lawn or the head of the player.
It is desirable that the ball used always exhibits the same characteristics in different external conditions. The players practicing the ball sport can then rely on the characteristics of the ball and are not surprised by changing characteristics. Among other things, this contributes to fairness and does not give the player, who has already been able to adjust to the changed characteristics, an advantage. Furthermore, the comparability of game results, which took place under different external conditions, is significantly increased if the sports device always exhibits the same characteristics.
For example, a football (i.e., soccer ball) is always to exhibit a uniform rebound, i.e. a football is always to bounce back to the same height from the same drop height on the same ground—independent of the external conditions, such as the ambient temperature for instance. It is expected of a golf ball that even at low temperatures in winter it does not harden and lose striking distance.
Weather conditions are in particular to be considered as external conditions, thus ambient temperature, humidity, air pressure and precipitation. These conditions particularly take effect in ball sports that are normally performed outside of a hall (“outdoor”), such as football (i.e., soccer), beach volleyball or golf. But different external conditions, such as ambient temperature, also occur in indoor sports (“indoor”) subject to and depending on the time of year or changes in the climate zone.
It has been determined, particularly with regard to the ambient temperature, that a ball is sometimes subject to substantial fluctuations in terms of its characteristics. Thus, for example at low ambient temperatures, a football will lose its elasticity, becomes harder and does not reach its usual airspeed when kicked. Also, its surface loses its adhesion—its grip slackens and the ball will bounce badly for the player. These observations apply equally to other sports balls. For example, at low ambient temperatures, a golf ball will lose distance and its trajectory cannot be controlled by means of handling the golf club as usual, since the adhesion between golf club and golf ball has changed. Furthermore, squash balls have to be brought up to a certain operating temperature during the game via unavoidable friction losses that occur hitting before the desired bounce characteristics set in. This problem worsens at lower ambient temperatures.
A further problem relates to the risk of injury, which is combined with the changed characteristics of the ball. For example, if a ball becomes harder for a sport, then injuries are more likely to occur. A football (i.e., soccer) player for instance is more likely to suffer a head injury when performing a header if the ball is harder. Since, as described above, balls cannot be controlled as well if their characteristics change, the risk of injuring other people when kicking or hitting the ball increases. For example, a non-participant could be hit by a mishit golf ball due to altered ball characteristics.
In order to counteract the problems listed above, balls were developed using special materials, which exhibit substantially constant material characteristics throughout a temperature range that is as broad as possible. As a rule, these are plastics or special rubber mixtures from which the balls or parts of balls, e.g. bladders or panels, are manufactured.
However, these materials only insufficiently solve the underlying problem. The temperature range of substantially constant material characteristics is still considerably smaller than the temperature range in which the ball sports are generally performed. In particular, footballs (i.e., soccer balls) are lacking a satisfactory solution for temperatures under 10° C. and the balls comprising the newer materials also change their characteristics here.
It is thus an object of the present invention to provide a ball for a ball sport that does not significantly change its significant characteristics and the behavior of which therefore remains predictable for the performance of the ball sport at low ambient temperatures. According to a further aspect of the invention, the suggested solution is not to influence the principle characteristics of the ball in a disadvantageous manner, i.e. is to maintain the same characteristics as a conventional ball at moderate ambient temperatures (such as a room temperature of roughly 20° C.). According to another aspect of the invention, the ball is to be manufactured in a manner that is as cost-effective as possible.